Although they have been in use since Vietnam, precision, laser-guided munitions (bombs, artillery shells and rockets) made their most public debut in the Gulf War of the early 1990s. Widely disseminated images of laser-guided munitions entering buildings through selected vent shafts or hitting bridges at specific structurally critical points gave the impression not only that a relatively small number of “smart” munitions could perform the same jobs that previously required carpet bombing or nuclear weaponry but also that collateral damage, and particularly civilian casualties, could be held to a minimum. The latest generation of laser-guided munitions is even more accurate and powerful than those used in the Gulf War and certainly represents the dominant trend in high precision aerial attack.
A laser-guided munition functions by homing in on a target illuminated (or “designated”) by a reflected spot of laser light. The laser light is modulated to distinguish it from other laser sources that may be nearby. A laser-seeking head mounted on the munition contains optical sensors that detect the reflected laser light. The laser-seeking head typically first acquires and verifies the reflected laser light at a distance of several miles. Thereafter, the head moves control surfaces on the munition to maintain the spot of reflected light within its “cross-hair.” As the munition closes on the target, the intensity of the reflected laser light amplifies significantly (roughly as a function of the square of the distance separating the target and the head).
Laser-guided munitions work best under ideal atmospheric conditions. Unfortunately, battlegrounds tend away from the ideal. Clouds, smoke, waves of hot air and intervening objects distort, obscure and attenuate the reflected laser light, making laser-designated target acquisition, verification and successful closure difficult. The consequence of failing to close to a target is either an unfulfilled military objective or collateral damage, both of which are unacceptable.
Testing of laser-seeking heads is therefore vital. Testing occurs in three phases. New designs of laser-seeking heads or new components for existing laser-seeking heads are advantageously design-tested under a wide variety of conditions to ensure that they will perform as designed. Newly manufactured laser-seeking heads are advantageously acceptance-tested to ensure that they have been correctly manufactured and calibrated. Laser-seeking heads that have been field-deployed are field-tested to ensure that they remain in good working order and proper calibration.
The best way to test laser-seeking heads is to provide to a laser-seeking head under test a simulation of the laser light that would be reflected back from a fictitious target. However, laser-designated target simulators do not have the luxury of replicating the actual distances involved. Instead, they are forced to use expensive laser light sources to provide the full range of, and proper increases in, light intensity that simulation requires. As a result, conventional target simulators are expensive, bulky and require extensive and time-consuming calibration to ensure proper operation.
What is needed in the art is a better laser-designated target simulator and a method of testing laser-seeking heads. More specifically, what is needed in the art is a laser-designated target simulator that does not require expensive laser light sources to provide the full range of, and proper increases in, light intensity.